vi 



fossils is only about twelve feet above the level of the sea. 

 This is evidently analogous to what has been termed the new- 

 er part of the Crag in England, and may be considered as the 

 equivalent of Brongniart's Gravier Coquillier, the effect of the 

 hist revolution anterior to the Diluvial epoch. 



The shells of this formation are 'sub-fossilized, and some of 

 them retain their colours ; they consist, in Maryland, chiefly of 

 the Pholas costata, Mactra laterally Area transversa, Nassa 

 triuittata, Ranella ca-udatu, &c. surmounted by a bed of Ostrea 

 Virginica, Similar deposits occur in North and South Caro- 

 lina ; and Brongniart has enumerated many localities in various 

 parts of the world, characterized by species which exist in the 

 neighbouring seas. One of the most interesting of these beds 

 occurs on the coast of Valparaiso, and consists of an entire 

 bank of the remarkable shell called Coucholepan, which still 

 inhabits the adjacent sea. A great part of this same coast 

 was suddenly elevated in 1822, exposing Oysters and Mytili, 

 attached to rocks then elevated from the sea ; hence it becomes 

 interesting to inquire whether or no similar causes, acting with 

 greater force and extent in the ancient world, may not have 

 been adequate to upraise the various beds of organic remains 

 to their present level above the ocean. 



With regard to the lowest of the Tertiary beds containing 

 organic remains, in the vicinity of Fort Washington, I may 

 remark that they are probably cotemporaneous with the supe- 

 rior strata of the Terrains Tritouit'iis (Calcaire grossier) of 

 Bronghiart. A characteristic shell of this formation is the Ve- 

 nerica-dia planicosta of Lamarck, a species I have discovered 

 in the deposit above mentioned, which also abounds in a largo 

 Turrit ella, never occurring in the upper or more recent beds. 



The 



banks of the Potomac, Kappahannock, James river and 



their tributaries, present in many places the same interesting 

 Geological features; being abrupt, composed of sand and clay 

 filled with testaceous relics, and so very friable, that immense 

 masses, loosed by the frost, frequently fall, strewing the mar- 

 gins of these rivers with the Pines which skirt their elevated 

 banksj thus at a place called the Rocks, on James River, a 

 few miles from the village of Smithfeld, it is difficult to walk 

 along the shore when the tide is in, on account of the fallen 

 trees, and masses of clay filled with innumerable shells. This 



Aote.-Puires vii uiul vill of this form of the Preface uro Idt-ntlcul with ii>. [17J ana 11H]7 



[22] 



